The overall objective of this proposal is to develop more effective diagnostic approaches to human breast cancer using monoclonal antibodies (MAb) reactive with breast carcinoma-associated antigens. We have developed a panel of MAbs, designated the DF series, prepared against membrane enriched fractions of a metastatic human breast carcinoma and MCF-7 cells. One of these, MAb DF3, has been further characterized and shown to recognize an antigen with a Mr of 300 kd. The DF3 antigen is detectable on the surface of human breast carcinoma cells and immunoperoxidase staining with MAb DF3 clearly distinguishes malignat and benign breast lesions. Double-determinant immunometric assays have been developed to monitor circulating DF3 antigen levels in patients with breast cancer. DF3 levels were elevated in 70% of patients with prior breast cancer. In contrast, only 6% of healthy women and less than 2% of patients with prior breast cancer who were free of disease after treatment had elevated DF3 antigen levels. Furthermore, DF3 antigen levels were shown to reflect changes in the clinical course of eight patients with metastatic breast cancer. The further evaluation of MAb DF3 in immunodiagnostic approaches to human breast cancer requires a more precise understanding of the immunochemical characteristics of DF3 antigen and factors affecting its expression (Specific Aim 1). This work should provide the basis for effectively using MAb DF3 in determining the prognostic value of immunoproxidase studies in primary human breast carcinomas (Specific Aim 2) and in monitoring clinical course by the radioimmunometric plasma assays (Specific Aim 3). A third immunodiagnostic approach will involve the use of radioiodinated MAb DF3 in lymphoscintigraphy studies to monitor for breast cancer involvement in axillary and internal mammary lymph nodes (Specific Aim 4). The remaining MAbs in the DF series (DF4, 7, 9, 15, 16) will be evaluated for: a) immunoperoxidase staining of fixed tissue slides; b) evaluation of the immunochemical properties, stability, affinity and cell surface expression of the DF antigens; c) circulation of the DF antigens and correlation with the clinical status in patients with breast cancer; and d) the utility of the DF Abs for radioimaging studies (Specific Aim 5). These studies should be important in gaining a better understanding of the biologic properties of DF breast carcinoma-associated antigens and in providing the basis for the use of the DF MAbs in the immunodiagnosis of human breast cancer.